1. Field of the Invention
The present invention relates to a method and related apparatus for improving continuous packet connectivity (CPC) for a user equipment in a wireless communications system, and more particularly, to a method and related apparatus for improving effects of CPC.
2. Description of the Prior Art
The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. Through the 3G mobile telecommunications system, a user can utilize a wireless communications device, such as a mobile phone, to realize real-time video communications, conference calls, real-time games, online music broadcasts, and email sending/receiving. However, these functions rely on fast, instantaneous transmission. Thus, targeting at the third generation mobile telecommunication technology, the prior art provides High Speed Package Access (HSPA) technology, which includes High Speed Downlink Package Access (HSDPA) and High Speed Uplink Package Access (HSUPA), to increase bandwidth utility rate and package data processing efficiency to improve uplink/downlink transmission rate.
For HSDPA and HSUPA, the 3rd Generation Partnership Project (3GPP) provides a continuous packet connectivity (CPC) protocol specification, which includes features that, for user equipments (UEs) in CELL_DCH state, aim to significantly increase the number of packet data users for a cell, reduce the uplink noise rise and improve the achievable download capacity for VoIP. For an HSDPA UE, the UE can work in a special mode, HS-SCCH less operation, included in CPC. Under this mode, a high speed shared control channel (HS-SCCH) is not transmitted with the first hybrid automatic repeat request (HARQ) transmission. In the HS-SCCH less operation, the UE receives a high speed physical downlink shared channel (HS-PDSCH) according to required control signals received when the HS-SCCH less operation is enabled, such as “channelization-code-set”, “modulation scheme”, “transport-block size”, “UE identity” and etc., for reducing HS-SCCH overhead for a HARQ process, thereby reducing UE power consumption.
For a detailed procedure for receiving the HS-SCCH, please refer to related communications protocol specification of 3GPP. If the UE did not detect consistent control information intended for this UE on any of the HS-SCCHs in the HS-SCCH set (the maximum size of the HS-SCCH set is 4) in the immediately preceding subframe (n−1), the UE shall in sub-frame n monitor all HS-SCCHs in the HS-SCCH set. On the other hand, if the UE did detect consistent control information intended for this UE in the immediately preceding subframe (n−1), it is sufficient in sub-frame n to only monitor the same HS-SCCH used in the immediately preceding subframe (n−1). This rule also applies in the HS-SCCH less operation.
If a UE detects that one of the monitored HS-SCCHs in sub-frame n carries consistent control information intended for this UE, the UE shall start receiving the HS-PDSCHs indicated by this consistent control information and perform decoding procedure. In addition, a cyclic redundancy check (CRC) in the last of each subframe of the HS-SCCH is utilized for verifying the UE identity and checking whether the decoding is successful. If CRC of the HS-SCCH is OK, that means the HS-SCCH subframe has been successfully received, otherwise, the HS-SCCH subframe has not been successfully received. When CRC of the HS-SCCH is failed, the information received on the HS-SCCH and the HS-PDSCH will be discarded.
As mentioned previously, in the HS-SCCH less operation, the UE receives and decodes information on the HS-PDSCH according to the control signals received when the HS-SCCH less operation is enabled whether the UE identity is correct. However, when the UE detects that one of the monitored HS-SCCHs in sub-frame n carries consistent control information intended for this UE, the UE starts receiving the HS-PDSCHs indicated by this consistent control information and performs decoding procedure. In this situation, the UE does not check whether the HS-SCCH less operation is enabled, and the UE does not decode information on the HS-PDSCH according to the control signals received when the HS-SCCH less operation is enabled. Finally, the UE may discard the information on the HS-SCCH and the HS-PDSCH because CRC of the HS-SCCH is failed. In fact, the information may be decoded successfully according to the control signals received when the HS-SCCH less operation is enabled and is not discarded.
In a word, in the prior art, when the UE detects that one of the monitored HS-SCCHs consistent control information intended for this UE, the UE starts receiving the HS-PDSCHs indicated by this consistent control information and performs decoding procedure, at the same time, the UE does not check whether the HS-SCCH less operation is enabled. The UE may lose the chance to decode the received information successfully according to the control signals received when the HS-SCCH less operation is enabled. Therefore, the effects of CPC are reduced.